Field
Embodiments described herein generally relate to plasma process apparatus.
Description of the Related Art
Inductively coupled plasma (ICP) process chambers generally form plasmas by inducing ionization in a process gas disposed within the process chamber via one or more inductive coils disposed outside of the process chamber. The inductive coils may be disposed externally and separated electrically from the process chamber by, for example, a dielectric lid. When radio frequency (RF) current is fed to the inductive coils via an RF feed structure from an RF power source, an inductively coupled plasma can be formed inside the process chamber from a magnetic field generated by the inductive coils.
In some chamber designs, the chamber may be configured to concentric inner and outer inductive coils. Due to constructive interference of the magnetic fields induced by the coils, the additive field properties between the inner and outer coils can result in non-uniformities in the distribution of the plasma formed at the substrate level away from the coils. For example, due to etch rate non-uniformity caused by the non-uniform distribution in plasma, a substrate etched by such a plasma may result in a non-uniform etch pattern on the substrate, such as an M-shaped etch pattern, e.g., a center low and edge low etch surface with peaks between the center and edge. Adjusting the power ratio between the inner and outer coils to control the severity of the non-uniformity is not sufficient to completely eliminate the non-uniformity.
Therefore, an improved plasma process apparatus is needed to better control plasma processing non-uniformity.